1. Field of the Invention
The present invention relates to a mesh structure. The present invention specifically relates to a mesh structure that has excellent adhesive force between uniaxially oriented bodies constituting the mesh structure and is suitably used as a reinforcing material.
2. Description of Related Art
Conventionally, a multilayer film prepared by laminating low-density polyethylene produced by high pressure radical polymerization on each side of a high-density polyethylene film is stretched and split to yield mesh film, then the mesh films are laminated in such a way that the orientation axes cross and are subjected to thermo-compression bonding, and consequently polyethylene nonwoven fabrics have been developed. Separately, the multilayer film is cut before or after stretching to give stretched tapes, then the tapes are woven, and consequently woven fabrics have been developed. These nonwoven fabrics or woven fabrics are used for bags for vegetables sold in shops, various bags, covering materials for agricultural use, and agricultural materials. In addition, such fabrics are integrated with other materials and are used for reinforced bags and tapes, for example.
Patent Document 1 discloses a method for producing a mesh nonwoven fabric that is produced by laminating a uniaxially oriented body (longitudinal web) made of a thermoplastic resin oriented in the longitudinal direction (length direction) on another uniaxially oriented body (lateral web) made of a thermoplastic resin oriented in the lateral direction (width direction). The mesh nonwoven fabric is produced as follows: a longitudinal web and a lateral web are separately prepared, then are overlapped each other, and are pressurized and heated to be integrated.
This kind of mesh nonwoven fabric has characteristics of light weight, good breathability, high strength in both longitudinal and lateral directions, excellent balance, and high toughness. The fabrics also have excellent characteristics of water resistance and chemical resistance.
[Patent Document 1] Japanese Patent No. 2983584
In recent years, in order to expand the application of mesh nonwoven fabrics to reinforcing materials and the like, there is a demand for mesh nonwoven fabrics having higher strength and higher adhesive force between uniaxially oriented bodies, for example, between the fibers constituting a longitudinal web and the fibers constituting a lateral web. As bag making has been performed at higher speed, there is another demand for improvement in low-temperature heat sealability and in the adhesive strength of a sealed portion. As the weights of containers and packing materials have been reduced, there is still another demand for lighter weight and higher strength. However, if having lighter weight, mesh nonwoven fabrics are more flexible and softer and have no rigidity or strength, which is one of the characteristics thereof. It is thus difficult to satisfy both light weight and high strength. On this account, weight reduction results in limitation of the application or poor processability such as bag making and creasing. In addition, the tensile strength is insufficient for reinforcement applications, and fibers constituting a uniaxially oriented body are peeled off. Thus, a practically sufficient reinforcement effect is not achieved in some cases.
A possible solution for reducing the weight and increasing the rigidity and tensile strength is that the thickness of the low-density polyethylene layer as the outer layer of a uniaxially oriented body is reduced and the ratio of the thermoplastic resin layer as the main layer is increased. However, when the thickness of each adhesion layer as the outer layer of the uniaxially oriented body is reduced, the adhesive force between the uniaxially oriented bodies is reduced, impairing the adhesive strength.